1. Field of the Invention
The present invention relates to negative angular forming dies for forming a thin metal plate and a pressing apparatus thereof. The term "negative angular forming dies" means forming dies whose upper die enters into its lower die from the lowering locus. The negative angular forming process in which a thin metal plate workpiece enters into the lower die from the lowering locus is generally carried out using a slide cam.
2. Description of the Background Art
In a conventional entering forming of a thin metal plate workpiece, the workpiece is placed on a lower die, an upper die is vertically lowered, and a follower cam of the lower die is driven by an operation cam of the upper die. The workpiece is worked from the lateral direction, and when the working is completed and the upper die rises, the operation cam is retracted by a spring.
In this operation, a forming portion of the follower cam which slides from the outer and lateral direction of the workpiece to form the workpiece is integrally formed into the same shape as that of a forming portion of the workpiece. However, since the forming portion of the lower die on which the workpiece is placed must be taken out from the lower die after the working is completed, the entering portion of the lower die must be divided and retracted, or a rear portion of the entering portion must be cut out so that the workpiece can be moved forward and the workpiece can be taken out. When the entering degree is small, there are no serious difficulties. However, when the entering degree is large, or when the workpiece is a part such as a thin metal plate front pillar outer of an automobile, having a long narrow frame-like cross section and having a groove shape, problems may occur. Since the groove width of the workpiece is narrow, if a portion of the entering lower die is divided or cut out, the shape of the workpiece is not clearly formed by the forming portion of the follower cam. Further, the strength of the lower die is insufficient, and it is difficult to carry out the entering forming.
Further, in the case of the entering forming by the slide cam, since the follower cam is allowed to slide for a long distance, it is not always easy to repeatedly slide the follower cam accurately at the specified position, and it is difficult to produce products of consistent quality.
Further, twisting or distortion occurs in the product and an adjustment of the product is sometimes required. However, in the case of a part having a three-dimensional curved surface, as in an outer plate portion of an automobile such as a side panel, a fender, a root a bonnet, a trunk lid, a door panel, or a front pillar outer, it is almost impossible to fix or adjust the product. In the case of assembling thin metal plates of the automobile, if twist or distortion occurs in the product, it is difficult to join the product to another part. It is also difficult to provide a thin metal plate structure of high quality, and to maintain a predetermined precision of the product of the thin metal plate molding.
If a slide cam is used, it is necessary to provide a large follower cam or heel on a side on which the workpiece of the lower die is placed. Therefore, the area of the lower die is increased, and the weight and the cost of the pressing dies are increased correspondingly.
To solve the above problems, a structure is proposed in which the lowering straight motion of the upper die is converted into rotational motion to rotate a columnar body, thereby forming a forming portion which enters into the lower die from the lowering locus in the straight direction of the upper die. The columnar body is subsequently rotated and retracted to a state in which the formed workpiece can be taken out from the lower die.
This configuration is shown in FIGS. 11 to 14. The negative angular forming dies include a lower die 102 having a supporting portion 101 on which a thin metal plate workpiece W is placed. An upper die 103 is lowered straight with respect to the lower die 102, and abuts against the workpiece W, forming the workpiece W. A groove 104 is opened at an outer peripheral surface in the axial direction, and an entering forming portion 107 enters from the locus of the upper die 103 and is formed on an edge of the groove 104 near the supporting portion 101. The lower die 102 is provided with a rotatable columnar body 106 and an entering forming portion 105. The upper die 103 is slidably provided with a slide cam 108 which is opposed to the columnar body 106, and the lower die 102 is provided with an automatic return tool 109 for rotating and retracting the columnar body 105 to a state in which the workpiece W can be taken out from the lower die 102 after the forming. The workpiece W is placed on the supporting portion 101 of the lower die 102, and along with the entering forming portion 105 of the columnar body 106 and the entering forming portion 107 of the slide cam 108, the columnar body 106 is rotated, and the slide cam 108 slides, thereby forming the workpiece W. After the forming, the columnar body 106 is rotated and retracted by the automatic return tool 109 so that the formed workpiece W can be taken out from the lower die 102.
The operation of this negative angular forming die will be described below.
First, as shown in FIG. 11, the upper die 103 is located at top dead center. At that time, the workpiece W is placed on the supporting portion 101 of the lower die 102, and the columnar body 106 is rotated and retracted by the automatic returning tool 109.
Next, the upper die 103 starts lowering, as shown in FIG. 12, and, a pad 110 first pushes the workpiece W against the supporting portion 101. Then, a lower surface of the slide cam 108 abuts against a rotation plate 111 such that the slide cam 108 does not interfere with the entering forming portion 105 of the columnar body 106, thereby rotating the columnar body 106 rightward as shown in FIG. 12.
When the upper die 103 continues lowering, the slide cam 108 (which is biased outwardly from the upper die) is moved leftward in the lateral direction by the operation of the cam against the biasing force of a coil spring 112, to assume a state shown in FIG. 13. The entering forming of the workpiece W is carried out by the entering forming portion 105 of the rotated columnar body 106 and the entering forming portion 107 of the slide cam 108.
After the entering forming, the upper die 103 starts rising. The slide cam 108 is biased outward from the die by the coil spring 112, and the slide cam 108 is moved rightward in FIG. 14 and rises without interfering with the entering formed workpiece W.
Because the slide cam 108 (which restricts the columnar body 106) rises, the columnar body 106 is rotated counter-clockwise by the automatic returning tool 109 as viewed in FIG. 14. When the entering formed workpiece W is taken out from the lower die 102, the workpiece W can be taken out without interfering with the entering forming portion 105 of the columnar body 106.
Even when the workpiece is changed straightly in the axial direction (a perpendicular direction with respect to the paper surface of FIG. 11) or is changed curvilinearly, if the amount of change is small (i.e., the radius of curvature is great), a wrinkle is typically not generated in the entering forming portion of the workpiece.
However, when the workpiece is changed curvilinearly in the axial direction and the amount of change is great (i.e., the radius of curvature is small), a wrinkle is generated in the entering forming portion of the workpiece.
FIG. 12 shows a state before the entering forming. As can be seen from FIG. 12, the entering forming portion 107 of the slide cam 108 merely pushes the workpiece W without pressing and clamping the workpiece W, thereby generating a wrinkle between the entering forming portion 105 of the columnar body 106 (when the workpiece is largely changed curvilinearly in the axial direction).
Although it may be effective to incorporate various mechanism into the rotating element for preventing the wrinkle from being generated, since the rotating element is extremely small, it is difficult to incorporate the various mechanisms.
A wrinkle is generated in the entering forming portion in the case of a so-called shrink flange forming in which a formed portion shrinks after forming, but the case of a so-called extending flange forming in which the formed portion extends after forming, the wrinkle is not generated.